The present invention relates to an integrating circuit which may be advantageously incorporated into an automatic exposure system for a camera.
In order to relieve photographers of the mundane task of setting the exposure dials on their cameras, automatic exposure systems have been developed. Such systems generally comprise a photosensor which produces an output voltage corresponding to the brightness of the scene being photographed. The camera shutter is opened at the instant the photosensor is energized. The output of the photosensor is integrated and the shutter closed when the integrated value reaches a predetermined level. This type of system may also be applied to electronic flash units for regulating the flash duration as a function of reflected light.
Since the output voltage of commercially available photosensors varies over a very wide rnage in accordance with incident light, it is desired to logarithmically compress the rangge of variation. Typical circuits for accomplishing this function generally comprise transistors and diodes which are very sensitive to temperature variations. Complex and relatively expensive circuitry is necessary for temperature stabilization of such circuits.